1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for recording a radiation image of an object, and reading out the radiation image to obtain electric image signals. This invention particularly relates to a radiation image recording and read-out apparatus wherein a tomographic image of an object is recorded on a stimulable phosphor sheet capable of storing the radiation energy.
2. Description of the Prior Art
As a method of obtaining a tomographic image of a desired tomographic layer of an object such as the human body, tomography has heretofore been known. In the tomography, a radiation source such as an X-ray tube and a radiographic film are positioned with the object intervening therebetween and are moved relative to each other at the time of irradiation of radiation around an arbitrary tomographic layer of the object so that the linear rule (specifying that the focal point of the radiation source, a point on the tomographic layer, and a point on the radiographic film be positioned on a straight line) and the geometric rule (specifying that the ratio of the distance between the focal point of the radiation source and the tomographic layer to the distance between the tomographic layer and the radiographic film be maintained constant) are satisfied. In this manner, only an image of a desired tomographic layer is formed on the radiographic film, and images of the other tomographic layers of the object are blurred. As a result, a radiation image of only the desired tomographic layer of the object is obtained. In the tomography, it is only necessary that the linear rule and the geometric rule be satisfied, and movements of the radiation source and the radiographic film may be carried out along any path, for example, a linear path, a circular path, an elliptic path, a spiral path, or a hypocycloidal path.
The applicant proposed a radiation image recording and read-out apparatus which can carry out tomography efficiently as disclosed in Japanese Unexamined Patent Publication No. 61(1986)-99138 (U.S. Pat. No. 4,762,999). Basically, the proposed radiation image recording and read-out apparatus comprises:
(i) a radiation source such as an X-ray tube for irradiating a radiation toward an object,
(ii) a circulation and conveyance means for conveying at least one stimulable phosphor sheet for recording a radiation image thereon along a predetermined circulation path,
(iii) an image recording section for disposing the stimulable phosphor sheet at an image recording position exposed to the radiation passing through the object, and recording a radiation image of the object on the stimulable phosphor sheet at the image recording position,
(iv) a movement means for moving the stimulable phosphor sheet and the radiation source at the image recording section relative to each other around an arbitrary tomographic layer of the object so that the linear rule and the geometric rule are approximately satisfied,
(v) an image read-out section disposed on the circulation path and provided with a means for irradiating the stimulating rays to the stimulable phosphor sheet carrying the radiation image stored thereon, and a photoelectric read-out means for detecting light emitted by the stimulable phosphor sheet exposed to the stimulating rays to obtain image signals, and
(vi) an erasing section disposed on the circulation path for, prior to the next image recording on the stimulable phosphor sheet for which the image read-out has been carried out at the image read-out section, having the stimulable phosphor sheet release the radiation energy remaining on the stimulable phosphor sheet.
The stimulable phosphor sheet will now be described below. When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor. The term "stimulable phosphor sheet" as used herein means a sheet-shaped recording material composed of the stimulable phosphor. In general, the stimulable phosphor sheet is composed of a substrate and a layer of the stimulable phosphor overlaid on the substrate. The stimulable phosphor layer comprises a binder and the stimulable phosphor dispersed therein. In the case where the stimulable phosphor layer is self-supporting, the stimulable phosphor layer itself can constitute the stimulable phosphor sheet. The stimulable phosphor sheet is described in detail in, for example, U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395. In the case where the stimulable phosphor sheet is utilized, a radiation image can be recorded at a higher sensitivity, a higher resolution and less distortion than in the case where the radiographic film is used.
With the aforesaid radiation image recording and read-out apparatus, a radiation image of the object is stored on the stimulable phosphor sheet by moving the stimulable phosphor sheet and the radiation source relative to each other in the manner as mentioned. The stimulable phosphor sheet is then exposed to stimulating rays such as visible light which cause the stimulable phosphor sheet to emit light in proportion to the stored radiation energy, and the emitted light is detected photoelectrically. In this manner, electric image signals representing the radiation image which was stored on the stimulable phosphor sheet are obtained. By use of the electric image signals, a tomographic image of the object can be reproduced.
However, the radiation image recording and read-out apparatus having the aforesaid configuration wherein the stimulable phosphor sheet is circulated and conveyed along the circulation path and sequentially sent to the image recording section, the image read-out section and the erasing section, has the drawback that the apparatus becomes large. Also, with the aforesaid conventional radiation image recording and read-out apparatus, it is necessary to carry out transfer of the stimulable phosphor sheet between the circulation and conveyance means for the stimulable phosphor sheet and the means for moving the stimulable phosphor sheet relative to the radiation source. To satisfy this requirement, the mechanism becomes complicated and the apparatus becomes larger.